Procter & Gamble, the Cincinnati-based company behind Pampers diapers and Tide detergent, reported a federal tax burden in 1969 that was 40 percent of its total profits, a typical rate in those days.

More than four decades later, P&G is a very different company, with operations that span the globe. It also reports paying a very different portion of its profits in federal taxes: 15 percent.

The world's biggest maker of consumer products isn't the only one. Most of the 30 companies listed on the country's most famous stock index, the Dow Jones industrial average, have seen a dramatically smaller percentage of their profits go to U.S. coffers over time, even as their share prices have driven the Dow to an all-time high.

A Washington Post analysis found that in the late 1960s and early 1970s, companies in the current Dow 30 routinely cited U.S. federal tax expenses that were 25 to 50 percent of their worldwide profits. Now, most are reporting less than half that share.

The reason is not simply a few loopholes tucked deep in the tax code. It's far bigger: the slow but steady transformation of the American multinational after years of globalization. Companies now have an unprecedented ability to move their capital around the world, and the corporate tax code has not kept up with the changes.

Just the opposite, in fact. Experts say the U.S. code has encouraged companies to shift their income overseas where it is more lightly taxed. Many firms, in turn, have discovered that just as they can move their manufacturing to other parts of the world, so, too, can they shift their income to far-flung tax havens such as the Cayman Islands.

The result is lower revenue here that could pay for infrastructure, education and other services that support domestic growth -- and that make life easier for U.S. firms.

As momentum builds for President Barack Obama and Congress to overhaul the corporate tax code, this steep decline in tax expenses as a share of profits is a critical factor in the debate. And increased globalization has made the task of fixing the tax code much more difficult than the country's last overhaul in 1986.

Company executives have complained for years that their firms face the highest tax burden in the world, citing the United States' 35 percent top corporate tax rate as the highest among developed economies.

P&G chief executive Bob McDonald was among 20 business executives -- including other leaders of Dow 30 companies such as General Electric's Jeffrey Immelt and Wal-Mart's Michael Duke -- who met with Obama in November to discuss the country's fiscal issues, including the tax code.

The country needs to "make our tax system more competitive and . . . reduce the corporate tax rate," said a statement from P&G ahead of the meeting.

Many companies argue that fixing the tax code would help improve economic growth, but that calculus has become more complicated as the interests of U.S. multinationals appear less neatly tethered to the interests of this country. This phenomenon has become especially clear during the economic recovery, with firms booking record profits while many American families still struggle with the wreckage from the Great Recession.

"When you get U.S. businesses coming to Washington and talking about, 'We need to do this and that for the U.S. economy,' what does that even mean?" said Doug Shackelford, a professor of taxes at the University of North Carolina's Kenan-Flagler Business School. "Who are they referring to? Is it U.S. workers? Is it U.S. shareholders?"

At first blush, the decline in corporate taxation could be a result of simple math. The top U.S. corporate tax rate -- that 35 percent that companies complain about -- is actually down from 48 percent in 1971.

But that's only part of the story.

A major factor is that profits earned abroad, which in theory are subject to the same U.S. tax rate, often are taxed much more lightly, and companies are earning more overseas than ever.

Of the 25 companies in the Dow 30 that break down their pretax income between domestic and foreign sources, 14 earned more money overseas than they did in the United States in the most recent annual filings available.

Any dollar earned abroad does not get taxed by the U.S. government until it flows back to the parent company. A J.P. Morgan report estimates there is $1.7 trillion of foreign earnings being held untaxed overseas by more than 1,000 U.S. firms.

Companies have also found ways to shift their income across national boundaries, roving from country to country in search of the lowest tax burden. Ed Kleinbard, a tax professor at the University of Southern California, has dubbed these moveable earnings "stateless income."

The trend has revolutionized company tax planning, especially in businesses that rely on intellectual property.